Rubber stabilized by a stannous complex of a phenolic compound



RUBBER STABILIZED BY A STANNQUS COM- FLEX OF. A PHENOLIC COMEOUND Harry E; Albert, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron,

Ohio, a corporation of Ohio No Drawing. Original a Serial No. 85,473, no dated January 27, 195 plication July 24, 1952, Serial 6 Claims.

1 This invention relates to the stabilization of rubbers and, more particularly, rubber-like copolymers of a conjugated diene monomer and a vinyl aromatic monomer, typified by GR-S. The

2,6-di-tertiary-butyl-p-cresol pplication April 4, 1949, w Patent No. 2,626,954, 2. Divided and this ap- 2 Salicylic acid. p-Hydroxy benzoic acid p-Aminophenol p-Nitrophenol conjugated diene monomers which may be used 5 Alpha-amino-beta-naphthol in,such copolymers include butadiene (by which Alpha-chloro-beta-naphthol is meant the compound butadiene 1-3) isoprene, 0-Ch1or0pheno1 Z-cyanobutadiene, cyclopentadiene, piperylene, p-Phenylphenol dimethylbutadiene, 2-methyl-l,3-pentadiene, etc. 4-tertiary-;b 1;y1-ml The vinyl aromatic monomers include styrene, p-Bromophenol nuclear-substituted styrenes, alpha-methylsty- Alpha-naphthol rene, monochlorostyrene, dichlorostyrene, vinyl- Beta-naphthol naphthalene, vinylbiphenyl, vinylcarbazole, 2- Tertiary-butyl-beta-naphthol vinyl-5-ethylpyridine, 2-ethyl-5-vinylpyridine, 1,5-dihydroxynaphthalene etc. The invention includes the new stabilizers, Hydroquinone their use in the rubber-like copolymers, and the Resorcinol stabilized FQ h The stannous salts used.- in the preparation of 'ghgolstgbgiizzrlsckmoi galleria? l i r lgi ml lgg l g the complexes are stannous salts of strong acids e andcletanno ,s

beta-naphthylamine, on aging discolor the 00- 2O mige, i s gi gg g g gl i g i polymer and hght'colored vulcftmzates prepared fonate, stannous toluene sulfonate, stannous from the 0013015 11181. These hght-colored vulnaphthalene sulfonate, etc

canizates are badly discolored when exposed to The following examples illustrate the prepare! ultraviolet light. The stabilizers of the present non of the complexes,

invention are nondiscoloring. They stabilize both the uncured copolymer and the vulcanizate. EXAMPLE 1 They are, therefore, advantageously; added 3(1) the STANNOUS COMPLEX 0F PHENOL emulsion of the copolymer obaine on em sion M copolymerization so that on coagulation they i t sodufn hydroxlde were are uniformly distributed in the coagulum and Ved m cu m cen lmeters and stabilize it during drying and subsequent treatt en i m of phenol W dlssolved 1n the gs; sggzfigg gi gga x53??? 3 53 22 timeters of water was added slowly during stir- Water-soluble stannous salt of a strong acid, a 3 2 f z g w filtered Washed: and

phenolic compound, and alkali in solution. They 9 T yleld was -0 m 5 are light-colored and, therefore, contain no tin pl eclpl ate a Whlte and when heated 9W an oxide which is a black compound. They conopen flame 1t decomposed before i It tain more tin than calculated for the tin salt underwent apparent h 9 heatmg one of the phenolic compound. Their structure is 40 hour at on analysls' 1t e d 61-02 unknown. They may be tin oxide polymers stag i of XIhereas qalgulatedfontent q bilized by the phenolic compound having a -fori i g j i 2, 3:; 2 2 g gi fi cent The mula' such as RO-Sn-O'Sn-OSnOI-I,

where R, is an aromatic residue. One of the ter-- EXAMPLE 2 minal hydroxyls in this suggested molecule may 5 STANNOUS COMPLEX OF BETA NAPHTHOL to someextent be replaced by chlorine or other v acid radical-depending upon the tin salt used SeVGIFtY'tWOEI'amS of betamaphthol re 6115- in producing the complex. There is little fact to solved 0119111591 of methanol to 111118 Was support such a suggested structure, and it may a e of ams of Yd X- be far fromthe actual Structure. 50 idem 200 cubic centimeters of water solu- The complexes may be produced from a phetlon. of 1 grams of Stannous chlorldeim 100 none compound such cubic centimeters of to per cent ethanol was then added slowly during stirring. The product Phenol was filtered and Washed twice with alcohol. It

pgTertiarywctylphenol was dried and found to weigh 43.3 grams. It was p-Cyclohexylphenol a light-cream-colored powder which decomposed p-Tertiary-butylphenol beforemelting on heating to a high'temperature,

Cresylic acid (a mixture of phenols derived from It underwent no apparent change when h t d petroleum), one hour at 150 C. A tin analysis-showed it to 4,6-dietertiary-butyl-m-cresol contain 67.10-percenttin. The calculated tin content of the normal salt is 29.3 per cent.

EXAMPLE 3 S'rANNoUs COMPLEX OF BETA-NAPHTHOL Thirty-six grams (.25 mol) of beta-naphthol and 56.4 grams of SnClz.2HzO (.25 mol) were dissolved in 300 cubic centimeters of 95 per cent ethanol. A solution of 20 grams (.5 mol) of sodium hydroxide in 250 cubic centimeters of 50 per cent ethanol was added very slowly during stirring. The product was filtered off, washed with alcohol and water, and then dried. It was a light-cream-colored solid which weighed 40 grams. It decomposed before melting on heating to a high temperature but underwent no apparent change when heated one hour at 150 C. The tin content was 73.10 per cent. The calculated tin content for the normal salt is 29.3 per cent.

EXAMPLE 4 STANNOUS COMPLEX OF O-CHLOROPHENOL Sixty-four and one-quarter grams of o-chlorophenol were dissolved in a solution of 20.6 grams of sodium hydroxide in 200 cubic centimeters of water. A solution of 47.4 grams of stannous chloride (anhydrous) in 100 cubic centimeters of water was added to this. An oily precipitate set tled to the bottom. It was washed by decantation and then separated from the water and dried. It was a white solid which decomposed before melting on heating to a high temperature over an open flame but, apparently, was stable when heated one hour at 150 C. The yield was 55 grams. It was found by analysis to contain 53.45 per cent tin. The calculated tin content of the normal stannous salt is 31.8 per cent.

EXAMPLE 5 STANNOUS COMPLEX 0F P-PHENYLPHENOL One hundred and seventy grams of p-phenylphenol were dissolved in one liter of 95 per cent ethanol. A solution of 40 grams of sodium hydroxide in 300 cubic centimeters of water was then added. A solution of 94.8 grams of stannous chloride (anhydrous) in 50 percent ethanol was added to the former solution slowly during stirring. The resulting precipitate was filtered, washed twice with 500 cubic centimeter portions of alcohol and once with water. The yield of dried product was 83 grams. It was a very light yellow solid which decomposed on heating to a high temperature on a spatula. It was, apparently, stable when heated one hour at 150 C. It was found to contain 64.15 per cent tin. The calculated tin content of the normal stannous salt is 25.9 per cent. The chlorine content was .36 per cent.

EXAMPLE 6 STANNOUS COMPLEX or P-CYCLOHEXYLPHENOL An alcohol-water solution of 52.8 grams of p-cyclohexylphenol and 24.0 grams of sodium hydroxide was prepared. To this was added, with stirring, a solution of 56.8 grams of stannous chloride (anhydrous) in alcohol. The precipitate was filtered and then washed with alcohol and water. The yield was 52.0 grams. The cream-colored product decomposed before melting when heated over an open flame. It underwent no apparent change when heated one hour at 150 C. It contained 75.85 per cent tin and 10.3 per cent chlorine. The calculated tin content for the normal salt is 25.3 per cent.

The ortho-dihydroxyphenols, such as catechol, form a compound analyzing close to the normal stannous salt when reacted with equivalent amounts of stannous chloride and alkali. However, the other polyhydroxy aromatic compounds, such as resorcinol, etc., form complexes which are much higher in tin than the normal salt. The following example is illustrative:

EXAMPLE 7 STANNOUS COMPLEX 0E HYDROQUINONE Fifty-five grams of hydroquinone and 112.8 grams of stannous chloride dihydrate were dissolved in one liter of water. A solution of 40 grams of sodium hydroxide in 150 cubic centimeters of water was slowly added until the solution was alkaline. This required about 75 per cent of the solution. After stirring a short time, the product was filtered. The yield was 78 grams. The product, a light-cream-colored solid, was, apparently, unchanged by heating one hour at 150 C. It decomposed on heating at a high temperature on a spatula. Analysis for tin showed it to contain 70.45 per cent. It contained 14.75 per cent chlorine. The calculated tin content for the normal salt is 52.3 per cent.

EXAMPLES 8-13 STANNOUS COMPLEXES OF PHENoLs PREPARED BY FOLLOWING GENERAL METHOD The following general method was employed in producing stannous complexes of:

p-Tertiary-octylphenol p-Cyclohexylphenol p-Tertiary-butylphenol Petroleum cresylic acid 4,6-di-tertiary-butyl-m-cresol 2,G-di-tertiary-butyl-p-cresol Three-tenths of a mol of sodium hydroxide (dissolved in water) was added to .3 mol of the phenol dissolved in per cent ethanol. Then .15 mol (28.4 grams) of anhydrous stannous chloride in ethanol-water was added slowly during stirring. The precipitate was filtered, washed with alcohol and water, and dried.

The complexes thus obtained were light in color and contained more tin than the normal stannous salts of these phenols.

In general, the procedure for the production of the stannous complexes may be given as reaction of the stannous salt with a phenolic compound and up to the equivalent amount of alkali. The amount of phenolic compound used may be varied over wide limits, and there is no harm in using a large excess (much greater than one molecular equivalent) and as little as 0.5 molecular equivalent of the phenol. Examples 3 and 6 illustrate the use of less than a molecular equivalent of phenol. Perhaps less than 0.5 molecular equivalent of the phenol would be suificient if conditions were properly controlled because only a small amount of phenolic material is combined in the tin complex. There should be at least substantially one molecular equivalent of alkali present for each molecular equivalent of the stannous salt.

It is preferable to use a solvent that is a solvent for all of the reactants. Suitable solvents include methanol, ethanol, dioxane, water, glycol, etc., and mixtures of these.

Although in the majority of the above examples the stannous chloride is added to the phenolic compound and alkali, Example 3 illustrates the mixing of the stannous chloride and the'phenolic compound before addition of the alkali.

The stabilizers of this invention referred to in the following tables were prepared according to the methods of the foregoing examples. The

beta-naphthol complex was prepared according to Example 2.

Table I COPOLYMER AGING Condition After Drying After Four Days at 90 C. After Two Days at 120 C. Antioxidant Color Hand Test T434 Color Hand'Test Color 'Hand'Test stannous complex of phenol white.-- no deterioration. 8.0 light brown unchenged. light brown. unchanged. staililnouls complex of o-chlorodo ..do 8. 0 .....do do do Do.

p eno stanncus complex of p-phenyl do lo 6.0 very light brown.v do do Do.

p eno phenlygl-beta-naphthylamine (eonbrown-.. .do 6. 6 brown do dark brown. 'somewhat'set up.

tro

The stabilizing effect of the tin complexes on GR-S, cured or uncured, when exposed to heat was tested. The vulcanizates were also exposed to ultraviolet light to evaluate their resistance to discoloration. They stabilize without appreciable discoloration. The following tests illustrate the stabilizing efiect and particularly as compared with phenyl-beta-naphthylamine, a stabilizer widely used commercially for such a rubber.

The first table compares the stabilizing eiTect of several complexes with that of phenyl-betanaphthylamine on drying latex coagulum which contains 2.per cent of stabilizer and also illustrates the stabilizing effect on aging at elevated 35 The data in the above table show the stannous complexes to be equal to phenyl-beta-naphthylamine on aging at 90 C. and superior onaging at 120 C. In color, all of the samples containing the stannouscomplexes are quite superior .to those containing phenyl-beta-naphthylamine. The samples were all coagulated from the copolymerization emulsion mixture by the use of aluminum sulfate low in iron.

The next table compares the stabilizin efiect of several of the complexes with-that of-phenylbeta-naphthylamlne when mixed with the emulsion resulting from the copolymerization reaction. Two per cent of the stabilizerwas used in each case.

Table II COPOLYMER AGING Antioxidant Condition After Drying, Color i and Hand Test Hand Test Alter Aging 4 Days at 90 Alter Aging 2 Days at 90 C 0., Color and Hand Test Color and stannous complex of beta-naphthol (prepared according to the process of Example 2).

stannous complex of beta-naphthol (prepared according to the process of Example 3).

stannous complex of 4,6-di-tertiary-b11tyl-m-cresol phenyl-beta-naphthylaminc cream color; no deterioration light yellow; no deterioration light redbi'own; no deterioration..

cream color; unchanged light brown; unchanged. brown; unchanged light yellow; unchanged.

cream color; unchanged.

light brown; unchanged. brown; somewhat set up.

sample to detect any stiffening, softening or other signs of deterioration. Tests recorded for the The results recorded in'the above table show the tin complexes to be superior to the control stabilizer, phenyl-beta-naphthylamine, on drying and under both conditions of aging.

It was found that a mixture of a phenolic compound and the stannous complex gave results somewhat superior to the use of either one alone. For convenience, the tests refer to mixtures of a complex and the phenol from which the "complex isprepared, but other phenols may be used. Stabilizing mixtures of phenols and complexes material aged 4 days include a test on the Fire- 6 are illustrated in the followingtable:

Table III COPOLYMER AGING After Drying 20v Hours at After Aging 4 Days at (1., After Aging 1 Day at 0.,

Ammxidam 0., Color and Hand Test Color and Hand Test Color and Hand Test 2. 2 G-di-tertiar -but l- -cresol yellow n0 deterioration-.. orange-yellow unchanged light brownset up. 2%, stannous cor i iplex of zo-di-tertiarylight biown; no deterioration. light yellow-brown; unchanged. light brown; sin-face slightly 'b t l- -creso1. resinous. 1% 2YG Ei-tertiary-butyl-p-cresol+1% very light brown; no deterioralight brown; unchanged light brown; unchanged.

stannous complex of same. tion. 2% stannous complex of beta-naphthoL. cream color; no deterioratlon light yellow; unchanged brown; surface somewhat resm ous.

beta-naphtho1+1% stannous comlight cream; no deterloration.-. cream; unchanged cream; unchanged plex of same.

brown; unchanged brown; somewhat set up.

b'eta-naphthol very light brown; no deterioration.

. The results recorded above show that the mixture of the phenol and stannous complex give better stabilization than either alone.

The next table shows the stabilizing effect of stannous complexes of polyhydroxy phenolic The aging was carried on for 10 hours in an air bomb at 260 F. under 60 pounds air pressure. The results of the tests show that compared to phenyl-beta-naphthylamine the stannous complex gave better retention of tensile on aging and compounds. The results of testing in a Fireabout the same elongation retention. stone extrusion plastometer are recorded as above. The following table records tests on the physical Table IV COPOLYMER AGING 2% starmous com- 27 hen HMS:

plex of hydro- 0 p y 2% Stalite g qumone naphthylamine Condition after drying hours at 75 0.:

T84 37.0 7.8 8.0. Color light cream brown green-gray. Hand test no deterioration"- no deterioration... no deterioration. Eeating 2 days at 110 0.:

T4} 18.8 71.6 26.4. Color... light brown brown. brown. Hand test unchanged unchanged slightly set up. Heating 4 days at 110 C.-

Tlfl 52.8 134.2 309.6. Color light brown brown brown. Hand test unchanged slightly set up"... set up.

The above data show that the stannous complex of hydroquinone is superior to phenyl-betanaphthylamine as a stabilizer for the uncured copolymer and show a definite superiority of the stannous complex as compared with Stalite (heptylated diphenylamine), a widely used stabilizer for GR-S.

The stabilizers were compounded with vulcanizing ingredients according to two formulae. In one formula channel black was used, and the results of the test with this formula show the effect of the presence of the stabilizer in an ordinary stock. The other formula contains no black and is heavily loaded with zinc oxide, titanium dioxide, and Calcene (a finely divided calcium carbonate supplied by Pittsburgh Plate Glass Company). Tests with this latter stock show the stabilizers of this invention to be nondiscoloring. In both formulae, GR-S copolymer was employed to which 2 per cent of the various stabilizers was added while the copolymer was still in the form of latex and before coagulation and drying.

Formula I Copolymer+stabilizer 100 Bardol Pine tar Stearic acid Zinc oxide Cyclohexyl benzothiazyl sulfenamide 1 Channel black Sulfur The Bardol of the above formula is a coal-tar plasticizer.

In the following table tests on the physical properties of different vulcanizates are recorded. The values are averages of those obtained on stock C. LOONU' CAJOOW properties of vulcanizates stabilized with 2 per cent of different stabilizers. The values given are averages of cures obtained at 280 for 40, 60, 80. and 120 minutes, respectively.

Table VI PROPE RTIES OF VULGANIZATE The above data show that the stabilizer used gives retention of modulus, tensile, and elongation on aging which is comparable to that given by the widely approved phenyl-beta-naphthylamine.

A further test was run to compare the stabilizing efiect of a different stabilizer with that of phenyl-beta-naphthy1amine. Two per cent of each stabilizer Was employed. The values recorded are the average of cures made at 280 F.1or 80 and minutes, respectively.

Table VII PROPERTIES or VULCANIZATE Staunous complex of ggfi gfi? as? me 200% Modulus Normal 610 740 Aged 1, 400 1, 950 Percent of Normal 229 264 Tensile:

Normal 2, 500 2, 700 Aged 2,125 2, 325 Percent of Normal. S5. 0 86. 2 Elongation:

Normal 570 520 Aged 275 240 Percent of Normal 47. 3 40. 2

The results show that the stannous complex is superior to phenyl-beta-naphthylamine from the standpoint of modulus retention and about equivalent in tensile and elongation retention.

In compounding the GR-S for tests in white stock, 2 per cent of various stabilizers was added to latex of GR-S copolymer before coagulation. The dried copolymer was then compounded as follows:

Formula II The Calcene is finely divided calcium carbonate produced by Pittsburgh Plate Glass Company. Accelerator #1 is cyclohexyl benzothiazyl sulfenamide. Accelerator #2 is tetramethylthiuram disulfide.

Samples of the white vulcanizate were cured 280 F. for 3G and 60 minutes, respectively, and then exposed in a fadeometer for 24 hours at 125 F. with the following results:

Table VIII VULCANIZATE AGING Color of Aged Antloxldant Vulcanizate 2% stannous complex of p-phenylphenol. slightly discolored. 1% 2,5-di-tertiary-butylp -cresol+l% very slightly discolored.

stannous complex of same. 1% beta-naphthol+l% stannous comslightly discolored.

plcx of same. 2% stannous complex of hydroquinone.. Do. 2% heptylated diphenylamine (control)- light brown. dikbeta-naphthyl-p-phenylenc diamine very dark brown.

contro The recorded results show that the stabilizers of this invention discolor only slightly as compared with two different commercial stabilizers and that the stabilizers of this invention may, therefore, be classified as nondiscoloring.

The foregoing is illustrative. The stannous complexes may be used alone or with a phenol. The stabilizers may be used not only for the stabilization of GR-S and other copolymers of conjugated diene monomer and vinyl monomer, but also natural rubber, etc. They may be added to the latex or compounded on the mill with dried latex coagulum or crepe, etc. They have particular value as nondiscoloring stabilizers for white GR-S or other copolymer of a conjugated diene monomer and a vinyl aromatic monomer.

This application is a division of my copending application Serial No. 85,473, filed April 4, 1949, which claims the stannous complexes and their preparation.

What I claim is:

1. The method of curing rubber and rubberlike copolymer of a conjugated diene monomer and a vinyl aromatic monomer which comprises heating the same with vulcanizing ingredients and as a stabilizer a phenolic compound and a stannous complex of a phenolic compound produced by reaction of a stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the normal stannous salt of the phenolic compound.

2. The method of curing rubber-like copolymer of a conjugated diene monomer and a vinyl aromatic monomer without substantial discoloration which comprises heating the same with vulcanizing ingredients including sulfur and as stabilizer a phenolic compound and a stannous complex of a phenolic compound produced by reaction of the stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the normal stannous salt of the phenolic compound.

3. The method of drying rubber-like coagulum of copolymer of butadiene and styrene without substantial discoloration which comprises heating the same while it contains adi .ixed therein sulfur and as stabilizer a phenolic compound and a stannous complex of a phenolic compound produced by reaction of the stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the stan nous salt of the phenolic compound.-

4. A substance of the group consisting of rubber and rubber-like copolymer of a conjugated diene monomer and a vinyl aromatic monomer stabilized with a phenolic compound and a stannous complex of a phenolic compound produced by reaction of the stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the stan nous salt of the phenolic compound.

5. Dried coagulum of rubber-like copolymer of butadiene and styrene which contains as a stabilizer a phenolic compound and a stannous complex of a phenolic compound produced by reaction of the stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the stannous salt of the phenolic compound.

6. Latex of a rubber-like copolymer of conjugated diene monomer and vinyl aromatic monomer which contains as a stabilizer a phenolic compound and a stannous complex of a phenolic compound produced by reaction of the stannous salt of a strong acid, an alkali and a phenolic compound of the class which consists of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, which complex contains more tin than the stannous salt of the phenolic compound.

No references cited. 

1. THE METHOD OF CURING RUBBER AND RUBBERLIKE COPOLYMER OF A CONJUGATED DIENE MONOMER AND A VINYL AROMATIC MONOMER WHICH COMPRISES HEATIANG THE SAME WITH VULCANIZING INGREDIENTS AND AS A STABILIZER A PHENOLIC COMPOUND AND A STANNOUS COMPLEX OF A PHENOLIC COMPOUND PRODUCED BY REACTION OF A STANNOUS SALT OF A STRONG ACID, AN ALKALI AND A PHENOLIC COMPOUND OF THE CLASS WHICH CONSISTS OF MONOHYDROXY AROMATIC COMPOUNDS AND POLYHYDROXY AROMATIC COMPOUNDS EXCEPT THOSE WHICH CONTAIN ORTHO HYDROXY GROUPS, WHICH COMPLEX CONTAINS MORE TIN THAN THE NORMAL STANNOUS SALT OF THE PHENOLIC COMPOUND. 